This invention is in the field of semiconductor processing and more specifically methods to clean semiconductor processing chambers and semiconductor processing chambers having improved cleaning.
In the chemical vapor deposition (CVD) process used to manufacture semiconductor wafers, the substrate (wafer) is heated in a chamber, activating a chemical reaction which deposits a film of material on the surface of the wafer. The CVD process typically occurs on the wafer as well as on the walls and other surfaces in the chamber. The film on the walls of the chamber and other surfaces must be removed to prevent the coating from flaking off and forming particles on the wafer which degrades wafer quality.
Certain areas of the walls of the chamber are heated more than other areas due to nonuniformity of output from heating lamps, different thicknesses of the walls, and other factors. Because of these nonuniformities, some areas of the chamber are coated more than other areas during the deposition process.
To remove the coating on the interior surfaces of the chamber, various cleaning methods have been developed. One cleaning method is a high temperature plasma or chemical etch using reactive species. A remote microwave plasma source (discussed, for example, in U.S. Pat. No. 5,082,517 (Moslehi)) or radio frequency (RF) radical generator may be used to activate a halogen containing gas. Radio frequencies are frequencies between about 10 kHz and about 300,000 MHz and are typically used in semiconductor processing to generate excited species, including radicals. These species are capable of removing deposits on various surfaces.
U.S. Pat. No. 5,454,903 (Redeker et al.) describes a method of cleaning the interior of a plasma etch reactor or a CVD reactor at pressures greater than 1.0 Torr by introducing an etchant gas such as NF3 and an electron donor gas such as helium into the chamber and applying RF power at megahertz frequencies.
U.S. Pat. No. 5,817,534 (Ye et al.) describes a method of cleaning a plasma reactor during plasma etching of a semiconductor wafer. This process involves using charged particles generated by a plasma during processing to remove contaminant particles at a rate which reportedly offsets the rate at which particles are deposited.
U.S. Pat. No. 5,879,575 (Tepman et al.) describes a method of cleaning a reaction chamber during plasma etching reactions by directing a portion of the plasma to the inner surface of the reactor using a rotating electrode.
The processes used to clean the surfaces of the reactor have disadvantages. A high temperature etch, with for example, HCl reduces the throughput of the chamber and contributes to premature wearing out of components in the reactor. A remote microwave plasma source is expensive and is not very efficient because of the substantial distance between the source and the surfaces to be cleaned.
None of the methods known to the art describe methods to locally clean selected portions of a reaction chamber.
Provided is a method of removing deposits from a substrate processing chamber, comprising:
(a) introducing into said chamber a first chemical capable of removing deposits upon application of RF energy; and
(b) applying RF energy to a coil located around selected areas of said chamber.
The coil is located around selected areas of the chamber, including those areas in the chamber which undergo greater deposition during substrate processing than other locations in said chamber. The coil may be disposed in various areas near or around the chamber, including near the inlet end of the substrate processing chamber, near the outlet end of the substrate processing chamber, near both the inlet end and the outlet end of the substrate processing chamber, near the bottom portion of the substrate processing chamber, near the top portion of the substrate processing chamber, near both the top and bottom portions of the substrate processing chamber, and other areas, as selected. The RF energy may be applied to various volumes of the chamber. For example, RF energy may be applied to less than about 75% of the total volume of the chamber, less than 50% of the total volume of the chamber, or less than 25% of the total volume of the chamber. The RF coil may be disposed around less than the entire chamber. For example, the coil may be disposed around less than 75% of the length of the chamber, less than 50% of the length of the chamber, or less than 25% of the length of the chamber, as needed or desired.
The first chemical can be introduced into the chamber in places coordinated with the location of application of RF energy. The selective RF field of this invention is not applied during substrate processing. It is applied as appropriate between steps of substrate processing. Typically, a cleaning cycle is periodically performed after one or more substrate processing cycles have been completed. A second chemical capable of removing deposits, either alone or in combination with said first chemical may also be introduced into the chamber. The second chemical can be introduced into the chamber in different locations than the first chemical. Also provided is a method of removing deposits from a substrate processing chamber containing a certain level of one or more chemicals capable of removing deposits comprising: introducing into a first area of said chamber a higher concentration of one or more chemicals capable of removing deposits, whereby the concentration of one or more chemicals is increased at a second area of said chamber. The first and second areas may be the same area, or may be different. There may be more than one first area and second area in a given chamber. Different chemicals may be introduced in different first areas.
The chamber may also be heated in combination with localized RF application. The areas in the chamber that are heated include those areas which undergo greater deposition during substrate processing than other locations in said chamber. Selected areas of the chamber may be heated by plasma generated by RF, or heating lamps, for example. The heating lamps may be infrared heating lamps and may direct energy to the entire chamber or to selected areas of the chamber.
Also provided is a method of cleaning a substrate in a substrate processing chamber, said method comprising:
(a) introducing a gas that generates radicals or other reactive species into said chamber that also contains a substrate;
(b) applying RF energy to a coil located around selected areas of said chamber.
This method may further comprise:
(c) depositing a desired substance onto said substrate.
Also provided is an apparatus with improved cleaning properties, the apparatus comprising:
(a) a substrate processing chamber having an inlet end and an outlet end and a top and a bottom portion;
(b) a coil capable of being coupled with an RF field, said coil being disposed at selected areas of said chamber; and
(c) a source of RF energy coupled with said coil; and
(d) a control for selective application of RF energy during a selected cleaning cycle.
The apparatus may also include a heat source, which directs more heat to certain areas locations of said substrate processing chamber than other areas of said substrate processing chamber. The heat source may be a lamp, and the lamp may emit energy in the infrared range.
As used herein, xe2x80x9cselected areasxe2x80x9d generally means areas where the placement of a coil, combined with an RF field, combined with one or more chemicals reduces the amount of deposited materials on the walls. xe2x80x9cSelected areas of the chamberxe2x80x9d to which the coil is located include areas where deposition of materials during substrate processing is higher than at other areas of said chamber. xe2x80x9cSelected areasxe2x80x9d may be upstream or downstream of the deposition. Placement of the coil and introduction of gases may be determined experimentally, by the methods described herein. Using the methods and apparatus described herein, the excitation source is much closer to the to-be etched surfaces than in other methods used for cleaning reactors, which results in a highly effective clean with application of lower RF powers. Using the methods and apparatus described herein, even short-lived H radicals can be effectively generated and transported in the gas stream to clean hydrocarbons, native oxide and other materials. The use of a remote plasma source does not offer these advantages.
Chemicals that may be used include gases. Some preferred gases are NF3, HCl, Cl2, H2, ClF3, F2, SF6, CF4, C2F6, other halogen-containing gaseous compounds and mixtures thereof, with NF3, HCl, Cl2 and H2 being more preferred. Any other gas or mixtures of gases that is capable of removing deposits upon application of RF energy may also be used. This gas or gases may be present in the chamber before application of RF energy, or gases may be introduced in the chamber during or after RF energy is applied. Other chemicals that are capable of removing deposits upon application of RF energy are included in the invention. The gas may also be diluted in an inert gas, or in a noble gas which, in a plasma, generates metastable species which effectively excite the cleaning gas. xe2x80x9cCleaningxe2x80x9d chemicals are typically only introduced into the chamber during cleaning cycles when the substrate is not present.
Chemicals are introduced into the chamber by means such as ports, valves, direct injection, and other means as known in the art.
As used herein, xe2x80x9cdepositsxe2x80x9d include any material that is present on a surface on or in a reactor that is desired to be removed. Deposits include, for example, a film of the substances used during CVD processing of a wafer or other workpiece that is present on the chamber walls or parts of the chamber walls. Deposits may also include other byproducts formed during substrate processing that are present in a reactor.
As used herein, xe2x80x9cremoving depositsxe2x80x9d indicates a reduction of the amount of deposits. It is not necessary for all deposits to be completely removed, and it is not necessary for deposits to be removed from all areas on or in the chamber.
Chambers capable of being used in the invention include plasma reactors, CVD reaction chambers and other chambers that experience deposition of material on the internal surfaces and are capable of having an RF coil in close enough proximity to cause excitation of chemicals and consequent removal of deposits. Chambers may be single-wafer reactors.
xe2x80x9cCoilxe2x80x9d or xe2x80x9cRF coilxe2x80x9d takes its meaning as known in the art. RF energy is applied to the coil using means known in the art, including matching networks and RF sources.
Frequencies that are useful in the invention to be applied to a coil include those included in the radio frequencies, preferably those frequencies between about 400 KHz and about 60 MHz. Frequencies include both those frequencies of greater than MHz and less than MHz.